As regards household appliances fed for instance with 110 or 220 volts, the plugs and sockets comprise two power conductors which as a rule are accompanied by a grounding wire. When the system includes such a grounding wire, it will be mounted on the socket and the orifice set aside for the plug in order to prevent any handling mistakes.
It was found early that the sockets may be dangerous to children who may insert metal objects (nails, screws, needles etc) into their orifices and thus may be electrocuted.
Accordingly it has already been suggested to mount protecting means on the sockets to render the orifice inoperative, said protective means being bypassed by the plug pins or by an additional control pin when the plug is inserted into the socket. Such devices fill two purposes: on one hand they safeguard the children from accidents and on the other hand they allow discriminating between appliances that can be hooked into a socket so fitted and those that must not be because only specific plugs comprise means to deactivate the orifice protecting means.
Illustratively, a household or shop may be equipped with electric power for all household appliances and various tools and further with special, ie "dedicated" electric power for sensitive equipment such as computers.
The French utility certificate 2,271,680 (Couqueberg) of 14 May 1974 discloses an electric-power connector comprising on one hand a socket with a mask sealing the socket orifices and thus making them inoperative, and on the other hand a plug which in addition to the two power pins also comprises an additional pin fitted with means to make the mask pivot to render the orifices accessible to the pins. This connector operates both as a safety and as a discrimination, i.e. a polarizing means, however a child still is able to rotate the mask.
The U.S. Pat. No. 4,494,809 (Soloman) of 22 Jan. 1985 combines the plug with an adapter controlling the insertion of a plug into a socket. This device allows discriminating between equipment to be hooked up, and that which must not be, to a given power source, but on the other hand it fails to provide safety to children.
As regards the system marketed by applicant as SECURIPRISE in 1982 and 1983, the means rendering the socket orifices inoperative are two contact pawls which will elastically retract from the orifices when in the inactive position and which are advanced into the active position by thrust means resting on the plug. These pawls are connected to the electric power source whereas the orifices are fitted conventionally with current conductors. By interrupting the electric power in their inactive position, said pawls thus inactivate the socket's orifices.
Similarly to the case for the Couqueberg document 2,271,680, the advantage of such a connector is that, with the thrust means resting on a fitting adaptable to the plug, the user was free to make use of it or to disregard it.
However it has been found that the safety function of such a connector is inadequate because a child might insert a curved metal object simultaneously into the two orifices and thus receive an electric shock. Furthermore this kind of connector does not meet present safety codes.
According to present safety codes, such a connector not only must provide that the two orifices be closed, i.e. inactive, when the plug has been withdrawn, but also the protection offered by the safety device must be preserved when an object is inserted into one of the two orifices.
The Luxembourg patent 67,675 (Niko P.V.B.A.) of 26 Jul. 1973 discloses a socket with a cover some distance from its front surface evincing orifices which are axially aligned with those of said front surface, the latter being linked to the power wires. A rotating mask is present between said cover and said front surface and comprises two flexible arms which are present between the socket's corresponding orifices and which are fitted with studs that may lock into one of the orifices of the front surface of the socket when the two arms are NOT jointly driven by the two plug pins. Such a connector meets the safety code but does not allow discriminating between two power sources.
Applicant moreover marketed a mask comprising two flexible arms fitted with studs and similar to the above described mask but sliding within the connector and elastically returning into the closed position between the matching orifices of said socket.
Again British electric power sources are known comprising masks fitted to be kept in their closed positions. Such systems are based on the principle that in British power sources, the grounding pin if any is borne by the plug and is longer than the pins connected to the electric conductors. As a result they cannot be adapted to those devices wherein the grounding pin is borne by the socket.